api mpms chapter 2.8b tank calibration

Manual of PetroleumMeasurement StandardsChapter 2—Tank Calibration

Section 8B—Recommended Practice for The Establishment of the Location of the Reference Gauge Point and the Gauge Height of Tanks on Marine Tank Vessels

FIRST EDITION, AUGUST 1995

American Petroleum Institute1220 L Street, NorthwestWashington, D.C. 20005

Copyright American Petroleum Institute Provided by IHS under license with API Licensee=Technip Abu Dabhi/5931917101

Not for Resale, 02/21/2006 21:39:24 MSTNo reproduction or networking permitted without license from IHS

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Manual of Petroleum Measurement StandardsChapter 2—Tank Calibration

Section 8B—Recommended Practice for The Establishment of theLocation of the Reference Gauge Point and the Gauge Height of Tanks on Marine Tank Vessels

Measurement Coordination

FIRST EDITION, AUGUST 1995

AmericanPetroleumInstitute



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SPECIAL NOTES

1. API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERALNATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE,AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED.

2. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYEES, MANU-FACTURERS, OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIPTHEIR EMPLOYEES AND OTHERS EXPOSED CONCERNING HEALTH ANDSAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONSUNDER LOCAL, STATE, OR FEDERAL LAWS.

3. INFORMATION CONCERNING SAFETY AND HEALTH RISKS AND PROPERPRECAUTIONS WITH RESPECT TO PARTICULAR MATERIALS AND CONDI-TIONS SHOULD BE OBTAINED FROM THE EMPLOYER, THE MANUFACTUREROR SUPPLIER OF THAT MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.

4. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE CONSTRUED ASGRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANU-FACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCTCOVERED BY LETTERS PATENT, NEITHER SHOULD ANYTHING CONTAINEDIN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINSTLIABILITY FOR INFRINGEMENT OF LETTERS PATENT.

5. GENERALLY, API STANDARDS ARE REVIEWED AND REVISED, REAF-FIRMED, OR WITHDRAWN AT LEAST EVERY FIVE YEARS. SOMETIMES AONE-TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THISREVIEW CYCLE. THIS PUBLICATION WILL NO LONGER BE IN EFFECT FIVEYEARS AFTER ITS PUBLICATION DATE AS AN OPERATIVE API STANDARD OR,WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION.STATUS OF THE PUBLICATION CAN BE ASCERTAINED FROM THE APIAUTHORING DEPARTMENT (TELEPHONE (202) 682-8000). A CATALOG OF APIPUBLICATIONS AND MATERIALS IS PUBLISHED ANNUALLY AND UPDATEDQUARTERLY BY API, 1220 L STREET, N.W., WASHINGTON, D.C. 20005.

Copyright © 1995 American Petroleum Institute



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iii

FOREWORD

The API Manual of Petroleum Measurement Standards (MPMS) is currently available.The manual will eventually include all subject matter now found in API measurementpublications—including evaporation loss measurement—as well as new material andrevised editions of existing MPMS material when revisions are completed.

API publications may be used by anyone desiring to do so. Every effort has been madeby the Institute to assure the accuracy and reliability of the data contained in them; however,the Institute makes no representation, warranty, or guarantee in connection with this publi-cation and hereby expressly disclaims any liability or responsibility for loss or damageresulting from its use or for the violation of any federal, state, or municipal regulation withwhich this publication may conflict.

Suggested revisions are invited and should be submitted to Measurement Coordination,Exploration and Production Department, American Petroleum Institute, 1220 L Street,N.W., Washington, D.C. 20005.



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v

CONTENTS

Page

SECTION 8B—RECOMMENDED PRACTICE FOR THEESTABLISHMENT OF THE LOCATION OF THEREFERENCE GAUGE POINT AND THE GAUGEHEIGHT OF TANKS ON MARINE TANK VESSELS

2.8B.0 Introduction........................................................................................................ 12.8B.1 Scope and Field of Application.......................................................................... 12.8B.2 References.......................................................................................................... 12.8B.3 Safety ................................................................................................................. 12.8B.4 Tank Measuring Equipment ............................................................................... 12.8B.5 Measurement Conditions and Tolerances .......................................................... 1

2.8B.5.1 Measurement Conditions............................................................................. 12.8B.5.2 Measurement Tolerances ............................................................................. 2

2.8B.6 Number and Location of Reference Gauge Points............................................. 22.8B.6.1 Number of Reference Gauge Points ............................................................ 22.8B.6.2 Location of Reference Gauge Points (Tank Ships) ..................................... 22.8B.6.3 Location of Reference Gauge Points—Combination Carriers (OBOs) ...... 32.8B.6.4 Location of Reference Gauge Points (Barges) ............................................ 3

2.8B.7 Gauging Hatches ................................................................................................ 42.8B.7.1 Primary Gauging Hatch............................................................................... 42.8B.7.2 Other Manual Gauge Points ........................................................................ 5

2.8B.8 Measurement Procedures ................................................................................... 52.8B.8.1 Preliminary .................................................................................................. 52.8B.8.2 Measurement of Gauge Point Locations ..................................................... 62.8B.8.3 Measurement of Reference Gauge Height .................................................. 72.8B.8.4 Expansion Trunk Cover Gasket Compression............................................. 7

2.8B.9 Calculation Procedures ...................................................................................... 8

Figures1—Longitudinal Section Through Typical Cargo Tank Showing Recommended

Gauge Point Locations for Tankers ........................................................................ 32—Transverse Section Through Typical Cargo Tank Showing Gauge Point

Locations ................................................................................................................ 43—Transverse Section Through Typical Cargo Tank Showing Recommended

Gauge Point Locations for Tankers ........................................................................ 54—Longitudinal Section Through Cargo Hold/Tank of a Combination Carrier

(OBO) Showing Recommended Gauge Point Locations ....................................... 65—Transverse Section Through Cargo Hold/Tank of a Combination Carrier

(OBO) Showing Recommended Gauge Point Locations ...................................... 76—Longitudinal Section Through Cargo Tank of a Typical Inland Waterway

Tank Barge Showing Recommended Gauge Point Locations ................................ 87—Transverse Section Through Cargo Tank of a Typical Inland Waterway

Tank Barge Showing Recommended Gauge Point Locations ................................ 98—Illustration of Length Between Draft Marks 70,000 DWT Tanker ...................... 109—Sketch for Locating Gauge Point.......................................................................... 1010—Check Measurement for Gasket Compression.................................................... 11



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2.8B.0 IntroductionThis document is intended to supplement the calibration

procedures described in API Chapter 2.8A, “Calibration ofTanks on Ships and Ocean-Going Barges,” and API Chapter2.7, “Calibration of Tanks on Barges” of the Manual ofPetroleum Measurement Standards (MPMS).

2.8B.1 Scope and Field of ApplicationThis recommended practice is intended as a guide for

establishing reference gauge heights during calibration ofmarine tank vessels. In many cases this calibration is carriedout by shipyard engineers who may not be fully familiarwith petroleum measurement requirements nor the use ofsuch measurements by petroleum inspectors and tanker oper-ating personnel. This procedure is also for recalibration ofvessels.

The importance of establishing an accurate referencegauge height for tanks on marine tank vessels cannot beoverstressed. Such tanks are generally calibrated in ullages(outages) whereas in measuring quantities remainingonboard (ROB) or free water, it is frequently more conve-nient and accurate to measure innages. The reference gaugeheight is a necessity in converting ullage to innage. Also, indetermining the volume of the ROB, the reference gaugeheight is a factor in every wedge formula, for the establish-ment of wedge tables.

API MPMS Chapters 2.7 and 2.8A provide three methodsof calibrating the volumes of tanks on marine tank vessels:calibration by linear measurement, liquid calibration, andcalibration from vessel drawings. The measurement andestablishment of the reference gauge height, however, canonly be determined by direct linear measurement.

2.8B.2 ReferencesUnless otherwise specified, the most recent editions or

revisions of the following standards, codes, and specifica-tions shall, to the extent specified herein, form a part of thisstandard.

APIManual of Petroleum Measurement Standards

Chapter 2.7, “Calibration of Tanks on Barges”Chapter 2.8A, “Calibration of Tanks on Ships and

Ocean-Going Barges”

DOT1

33 Code of Federal Regulations

IMO2

Resolution of the International Conference on TankerSafety and Pollution Prevention

NFPA3

306 Control of Gas Hazards on Vessels

2.8B.3 SafetyPrior to entering any compartment, permission must be

obtained from the vessel’s master, senior deck officer, autho-rized shipyard official, or other responsible person in charge.This responsible person should be able to supply informationregarding particular materials and conditions or the appli-cable Material Safety Data Sheet. Before entering thecompartment, a valid marine chemist’s certificate must beobtained indicating that the compartment is “Safe forWorkers” and/or “Safe for Hot Work,” as prescribed inNational Fire Protection Association 306, Control of GasHazards on Vessels. Regulations of the U.S. Coast Guard,the Occupational Safety and Health Administration (OSHA),or other international, federal, state, or local regulations mayalso apply. Such testing must be made at least every 24 hoursor more often when changing conditions warrant.

When entering a compartment, another person shouldstand watch at the compartment entrance for the duration ofsuch entry to sound an alarm should an emergency occur.Normal safety precautions with respect to staging andladders are to be observed.

2.8B.4 Tank Measuring EquipmentTank measuring equipment for the establishment of the

reference gauge point location and reference gauge heightshall be as described in 2.8A.7.1 of API MPMS Chapter2.8A or 2.7.7.1 of API MPMS Chapter 2.7.

2.8B.5 Measurement Conditions andTolerances

2.8B.5.1 MEASUREMENT CONDITIONS

Measurements should be taken only after all construction,conversion, and repair activities that would affect tank orreference height dimensions have been completed.

Chapter 2—Tank Calibration

SECTION 8B—RECOMMENDED PRACTICE FOR THE ESTABLISHMENT OF THE LOCATION OF THE REFERENCE GAUGE POINT AND THE

GAUGE HEIGHT OF TANKS ON MARINE TANK VESSELS

1

1U.S. Department of Transportation. The Code of Federal Regulations isavailable from the U.S. Government Printing Office, Washington, D.C.20402.2International Maritime Organization, London, England.3National Fire Protection Association, 1 Batterymarch Park, Quincy,Massachusetts.



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2 CHAPTER 2—TANK CALIBRATION

The area of the tank bottom directly beneath the referencegauge point must be a clean surface and free of scale, debris,and solid or semi-solid petroleum residues.

When measurements for the reference gauge height aremade, the vessel should be on an even keel with no trim orlist. If this is not feasible, a correction must be applied to themeasured gauge height to obtain the corrected referencegauge height as described in API MPMS Chapter 2.8A.

2.8B.5.2 MEASUREMENT TOLERANCES

Measurement tolerances shall be as described in 2.8A.8.2of API MPMS Chapter 2.8A or 2.7.8.2 of API MPMSChapter 2.7.

2.8B.6 Number and Location ofReference Gauge Points

2.8B.6.1 NUMBER OF REFERENCE GAUGEPOINTS

In the United States, all tank vessels fitted for crude oilwashing (COW) are required to have four hand gauging loca-tions in each tank, one of which is to be located in the aftermostportion of the tank, as per U.S. Coast Guard regulations.

Note: U.S. Coast Guard Regulations 33 CFR 157.128 (b) state (in connec-tion with design, equipment, and installation for COW), “Each cargo tankmust be designed to allow the level of crude oil in the tank to be determinedby: (1) Hand dipping at the aftermost portion of the tank and three otherlocations; or (2) Any other means acceptable to the Commandant.”

This wording is taken from Section 4.4.4 of Resolution of the Interna-tional Conference on Tanker Safety and Pollution Prevention, 1978 of theInternational Maritime Organization.

The regulations make no requirement that each of thesehand gauging points be calibrated for the total and incre-mental volume of the liquid in the tanks.

Each tank on self-propelled tank vessels shall be fittedwith a minimum of two principal reference gauge points,each fully calibrated for total and incremental tank volume.The additional manual gauging points are required by COWregulations. The reference gauge heights at these additionalhatches may be established for flexibility in measurements,for example, quantities remaining on board (ROB) and/oronboard qualtities (OBQ). Nonself-propelled inlandwaterway barges may require a total of three calibratedprimary reference gauge points as covered in 2.8B.6.4.

The location of the primary reference gauge points and theadditional secondary (manual) gauging points are covered in2.8B.6.2 for conventional tankships and in 2.8B.6.3 forCombination Carriers [Ore/Bulk/Oil (OBOs)].

2.8B.6.2 LOCATION OF REFERENCE GAUGEPOINTS (TANK SHIPS)

The two calibrated reference gauge points referred to in2.8B.6.1 should be located in each tank as follows.

The primary reference gauge point may be located at the

geometric center of the tank at deck level. This position willeliminate the effect of trim and list on the calculation ofstatic volumes when the vessel is in a loaded condition.

However, if a swash bulkhead or transverse web frame isfitted at the mid length of the tank, the reference gauge pointmust be sufficiently forward of the mid length so that the zerogauge point clears the swash bulkhead or web frame at thebottom under the normal direction of maximum trim. Thislocation will permit obtaining an ullage for a quick closeapproximation of tank content volume without the necessity ofapplying a trim correction. For complete accuracy, a trimcorrection is necessary inasmuch as the gauge point has beendisplaced longitudinally from the geometric tank center.

The secondary reference gauge point or points on a vesseltank should be located at the aft and/or forward end of thetank, depending on the varying operating trim conditions.

Note: In the course of normal operations involving a barge that operateswith trim by the bow and stern, the primary gauge point at the geometriccenter is not required since secondary gauge points are required at bothforward and aft locations.

This gauge point should be located as close to the aft orforward bulkhead, centerline, or inboard bulkhead aspossible, but again sufficiently forward of same so that agauge tape suspended to take OBQ/ROB/free water measure-ments does not contact the bulkhead.

The additional manual gauge points may be fitted at anyconvenient location in the tank where there is a clear drop tothe bottom.

The recommended fore and aft locations for the referencegauge points and the manual gauge points are shown inFigure 1. Figure 2 shows the same tank in a transversesection, indicating the necessity for clearance of the gaugepoint from the tank structures.

The secondary reference gauge point at the aft end of eachtank should be as far in board as possible so that if deadriseis present, the volume of cargo below the zero gauge pointwill be minimized. This is particularly necessary for wingtanks at the forward and aft ends of the tank space.

Figure 3 indicates the recommended transverse locationsfor the reference and additional gauge points. With the usualconfiguration of tank structure, it may not be possible tolocate a primary reference gauge point at the geometriccenter of a center tank due to the presence of the centerlinedeck girder and the center vertical keel at the bottomrequiring the gauge point to be offset slightly to one side orthe other. For the wing tanks, there is usually no problem inlocating a gauge point at the mid width of the tank.

All gauge points on all types of tank vessels must have aclear path from the reference gauge point to the zero gaugepoint clear of all interferences throughout the expected rangeof trim and list. This would include, without limitation,clearances from all structural framing members as alreadynoted, piping, ladders, heating coils, reach rods, and anodes.



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SECTION 8B—ESTABLISHMENT OF THE LOCATION OF THE REFERENCE GAUGE POINT AND THE GAUGE HEIGHT OF TANKS 3

2.8B.6.3 LOCATION OF REFERENCE GAUGEPOINTS—COMBINATION CARRIERS(OBOs)

The same general principle for location of reference gaugepoints applied to conventional tankers should apply equallywell to OBOs, namely one primary reference gauge point asclose as possible to the geometric center of each tank, in planview, and one secondary reference gauge point at the aft endof each tank to evaluate ROB. However, due to the widevariety of tank/hold configurations on OBOs, specificrecommendations become difficult. Figures 4 and 5 depictthe longitudinal and transverse sections through a represen-tative cargo hold/tank.

For an OBO with one hatch per hold, the recommendedprimary reference gauge point at the geometric center of thetank can be located on the hatch cover at the mid length ofthe tank as shown in Figure 4. If the hatch cover is of the twopanel side rolling type with a centerline joint, the primaryreference gauge point must be offset slightly to one side ofthe mid width of the tank to clear such joints as depicted inFigure 5. The secondary reference gauge point at the aft endof the hold/tank must be kept clear of sloping bulkheadsforming the lower ballast tanks.

OBOs are required to have a sounding tube for use whencarrying dry bulk cargoes. This may be counted as one ofthe manual points required for COW. This sounding tubewill be calibrated in innage; however, the gauge heightshould be measured and recorded for convenience inconverting between innage and ullage. Sounding tubesmust be slotted.

2.8B.6.4 LOCATION OF REFERENCE GAUGEPOINTS (BARGES)

Barges without propelling machinery are not subject to theextremes of trim as are tankships with machinery aft. Theymay, however, be subject to trim either forward or aft, whichwould require calibrated secondary gauge points at each endof each tank to evaluate ROB.

Location of a calibrated primary reference gauge point onthe exact geometric center of the tank, in plan view, mayhave the same problem with interference from tank structureas on tankships.

For a barge, these primary reference gauge points may becalibrated as ullages or as innages. If calibrated as innages,they may very well be as sounding tubes with strike plates.These sounding tubes must be slotted.

Deck

Bottom

Reference Gauge Point Primary Gauge Point(At or near tank center)

AdditionalHand Gauging

Points

Center Tank Wing Tank

Cen

terli

ne o

f Shi

p

Tape Path

Zero Gauge Points



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Since inland waterway tank barges are not fitted for COW,additional hand dipping (hand gauging) points may not berequired.

Recommended locations for reference gauge points oninland waterway tank barges are indicated in Figures 6 and 7.

2.8B.7 Gauging Hatches

2.8B.7.1 PRIMARY GAUGING HATCH

For many years, the common practice has been to fit thegauging hatch in the dome of the expansion trunk cover(access hatch cover). This introduces an error in the gaugeheight due to compression of the hatch cover gasket. With a 2inch square gasket, the error may be as much as 1⁄2 inch aftermany openings and closings. For this reason, future installa-

tions should locate the primary gauging hatches on standpipesseparate and apart from the expansion trunk cover.

The standpipe should be a length of extra heavy pipeextending from the deck to a suitable height above the deck,and at least one standpipe per tank should have an internaldiameter sufficient to pass a sample container.

All reference gauge points should be calibrated for incre-mental tank volumes, have trim and list correction tables,and have a reference gauge height established.

The upper end of the standpipe may be fitted with ahinged dogged cover. If a hinged cover is fitted, the refer-ence gauge point should be established as the rim of thestandpipe opposite the hinge.

If the vessel is fitted with a vapor lock system on thestandpipes and positive inert gas pressure must be main-

Bottom

Deck


Reference Gauge Point

Tape Path

Cen

terli

ne o

f Shi

p

Zero Gauge Points

Figure 2—Transverse Section Through Typical Cargo Tank Showing Gauge Point Locations and Tape Path



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tained throughout the gauging process, a closed gaugingdevice must be utilized. The reference gauge point will be tothe top of the indicator bar on the gauging device. The refer-ence gauge height will be established with the closedgauging device in operating position.

If a screw-down plug is fitted, the reference gauge pointshould be established to the top lip of the plug and clearlyindicated by scribe marks on the deck of the vessel.

2.8B.7.2 OTHER MANUAL GAUGE POINTS

Other manual gauge points may have closures similar tothose on principal gauge hatches or they may simply be adrilled and tapped opening in the deck or in the cover for aportable tank cleaning machine, closed by the pipe plugwhen not in use. These additional openings for manualgauging need only be calibrated for a reference gauge point.

2.8B.8 Measurement Procedures

2.8B.8.1 PRELIMINARY

Prior to boarding the vessel, the vessel’s drafts should beread, fore, aft, and amidships and port and starboard, using asmall boat as necessary. Vessel personnel should becontacted to ensure that there will be no change in ballast,bunkers, or cargo during the measurement process.

The presence of list should be checked by noting thedifference in drafts at the midship port and starboard draftmarks. If at all possible, the list condition should becorrected to zero list condition. If list is present, it should berecorded as port or starboard.

Ensure that neither hog nor sag condition exists by acomparison of the observed drafts. See API MPMS Chapter2.8A, Appendix B for definition of these conditions.

Deck

Bottom

Reference Gauge Point Primary Gauge Point(At or near tank center)

AdditionalHand Gauging

Points


Cen

terli

ne o

f Shi

p

Tape Path

Zero Gauge Points

Figure 3—Transverse Section Through Typical Cargo Tank Showing Recommended Gauge Point Locations for Tankers



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To correct the reference gauge heights for the vessel in anuneven keel condition, the length of the vessel between draftmarks should be obtained, either from the vessel’s docu-ments or by measurement. The measurement is obtainedfrom reading the drafts on the vessel’s sides, then obtainingthe distances from the draft marks to the forward and aftperpendicular as indicated in Figure 8.

At each gauge point, an innage tape should be loweredand the tape clamped in place at the reference gauge pointwith the bob at the zero gauge point. The tank should then beentered and the tank bottom, in way of the zero gauge point,examined for cleanliness. If the condition is not consideredsatisfactory, measurement procedures should be suspendeduntil proper cleanliness is obtained.

The tape path for the full height of the tank should becarefully examined for clearances from tank internals. If it isconsidered that an incipient interference may occur at somecondition of trim or list, a notation of such interference andspecific conditions of trim and list involved should beincluded in the capacity tables.

2.8B.8.2 MEASUREMENT OF GAUGE POINTLOCATIONS

The location of each gauge point in the longitudinal andtransverse directions shall be carefully measured fromconvenient longitudinal and transverse bulkheads andrecorded. A sketch locating each gauge point shall beprepared similar to Figure 9. The sketch shall also indicatethe type of gauge hatch fitted, whether it be on the expansiontruck cover, on a standpipe with hinged cover, on a standpipewith vapor lock, on a pipe plug in the deck, or in the cover ofan opening for a portable tank cleaning machine.

With more than one calibrated reference gauge point pertank, it is essential that the vessels’s capacity tables beclearly specific as to which reference gauge point the tableapplies. It is recommended that the following terminology beused: “Center Tank No. 6 Forward,” “Port Wing Tank No. 4Mid,” “Starboard Wing Tank No. 5 Aft.”

Likewise, if calibration information plates are installed inaccordance with 2.7.13 of API MPMS Chapter 7.2 or2.8A.13 of API MPMS Chapter 2.8A, the designation of

Hatch CoverScrewed Plug

at Deck

Additional HandGauging Points

Secondary Reference Gauge Point(Near aft end of tank)

Deck

Primary Reference Gauge Point(Near center of tank)

SoundingTube

Aft

Bul

khea

d

For

war

d B

ulkh

ead

Cargo Hold/Tank

Tape Path

Inner Bottom

BottomZero Gauge PointsWater Ballast Tank

Figure 4—Longitudinal Section Through Cargo Hold/Tank of a Combination Carrier (OBO) Showing Recommended Gauge Point Locations



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each reference gauge point must clearly correspond with thedesignation in the capacity tables.

2.8B.8.3 MEASUREMENT OF REFERENCEGAUGE HEIGHT

Using a calibrated working tape for height measurementas described in 2.8A.7.3 of API MPMS Chapter 2.8A, thedistance from the zero gauge point to the reference gaugepoint is measured for each gauging location. These arerecorded as the measured gauge height and noted in thecapacity tables.

2.8B.8.4 EXPANSION TRUNK COVER GASKETCOMPRESSION

When measuring the reference gauge height on anexisting vessel having the gauge hatch in the expansion trunkcover, the cover must be dogged down as in normal opera-tion. With the cover in this position, a check measurementshould be made from the lip of the cover to the deck. As thisdimension will vary around the circumference of the expan-sion trunk due to the deck camber, the measurement shouldbe taken in line (longitudinally)” with the reference gaugepoint as shown in Figure 10.

Hatch CoverAdditional HandGauging Point

Sounding Tube

Primary Reference Gauge Point(At or Near Center of Tank)

Secondary Referece Gauge Point(Near Aft Bulkhead)

Deck

Tank Path

Zero Gauge Points

Inner Bottom

Water Ballast Water BallastPipe Duct

Center Line Bottom

Cargo Hold/Tank

Figure 5—Transverse Section Through Cargo Hold/Tank of a Combination Carrier (OBO)Showing Recommended Gauge Point Locations



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The measured gauge height and ullages will then becorrect for that particular gasket compression, and thisshould be noted in the capacity tables.

As an alternative, it is recommended to attach a smallhorizontal plate on the expansion trunk and a second plate onthe lip of the cover immediately above—the two plates beingless than 6 inches (15 centimeters) apart. The plate on thecover shall have a horizontal line scribed upon it. At the timeof measuring the reference gauge height, the distance fromthe horizontal line to the scribed line is also measured. Thisdistance then becomes the compression distance; it isprecisely measured to the nearest millimeter and recorded at

the time of calibration. The measured gauge height andullages will then be correct for that particular gasketcompression, and this should be noted in the capacity tables.

2.8B.9 Calculation ProceduresIf the vessel was at an absolute even keel at the time of

measurement with no trim or list, then the measured gaugeheight is the reference gauge height and no further correc-tions are necessary. However, if at the time of measurement,trim, list, or both are observed, the measured referenceheight must be corrected for trim, list, or both using guide-lines as detailed in 2.8A.10.4 of API MPMS Chapter 2.8A.

Secondary Reference Gauge Point(Near end of tank)

Primary Reference Gauge Point(Near center of tank)

Deck

Aft

Bul

khea

d

For

war

d B

ulkh

ead

Cargo Tank

Tape Path

Zero Gauge Points Bottom

Figure 6—Longitudinal Section Through Cargo Tank of a Typical Inland Waterway Tank Barge Showing Recommended Gauge Point Locations



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Secondary Gauge Point(Near Centerline Bulkline

and Aft Bulkhead)

Primary Reference Gauge Point(Near Center of Tank)

Deck

Cargo Tank

Tank Path

Cen

terli

ne B

ulkh

ead

Zero Gauge Points Bottom

Baseline

Figure 7—Transverse Section Through Cargo Tank of a Typical Inland Waterway Tank Barge Showing Recommended Gauge Point Locations



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Length Between Draft Marks = 232.77 m

Length Between Perpendiculars = 240.00 m

5.26 m 1.97 m

AFT Draft Marks FWD Draft Marks

AFT Perpendicular FWD Perpendicular

Figure 8—Illustration of Length Between Draft Marks 70,000 DWT Tanker

Centerline of Ship or Longitudinal Bulkhead

Gauge Hatch

Reference Gauge Point on Standpipe36˚ Above Deck With Vapor Lock System

Tra

nsve

rse

Bul

khea

d or

Web

erfr

ame

No.

Figure 9—Sketch for Locating Gauge Point



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Expansion Trunk

Scribe MarksDistance

Gauge Hatch

Reference Gauge Point to Top LipInside of Gauge Hatch

Opposite Hinge

Gasket

CheckMeasurement

Deck

Figure 10—Check Measurement for Gasket Compression



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1-01102—8/95—5C ( )



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American Petroleum Institute1220 L Street, NorthwestWashington, D.C. 20005

Order No. H028B1



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api mpms chapter 2.8b tank calibration

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